JP3870060B2 - Image heating device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an electromagnetic (magnetic) induction heating method.Statue ofHeating equipmentIn placeRelated.
[0002]
[Prior art]
An image heating and fixing device in an image forming apparatus such as an electrophotographic copying machine, a printer, or a fax machine will be described as an example.
[0003]
An image heating and fixing device in an image forming apparatus is a toner (developer) made of heat-meltable resin or the like by an appropriate image forming process means such as electrophotography, electrostatic recording, and magnetic flux recording in an image forming unit of the image forming apparatus. ) To heat and fix an unfixed toner image formed on the surface of the recording material by a direct method or an indirect (transfer) method as a permanently fixed image on the surface of the recording material.
[0004]
Conventionally, as such an image heating and fixing apparatus, there are various apparatuses such as a heat roller system, a film heating system, and an electromagnetic induction heating system.
[0005]
a. Heat roller method
This consists of a rotating roller pair of a fixing roller (heat roller) and a pressure roller that are heated and adjusted to a predetermined fixing temperature by incorporating a heat source such as a halogen lamp, and a pressure nip (fixing nip) of the roller pair. In this case, an unfixed toner image is heated and fixed on the surface of the recording material by introducing a recording material on which an unfixed toner image is formed and supported as a material to be heated.
[0006]
However, this apparatus has problems such as a large heat capacity of the fixing roller, a large amount of electric power required for heating, and a long wait time (waiting time from when the apparatus is turned on until a print output is enabled). Further, since the heat capacity of the fixing roller is large, there is a problem that a large amount of power is required to raise the temperature of the fixing nip portion with limited power.
[0007]
As a countermeasure, the thickness of the fixing roller is reduced to reduce the heat capacity of the fixing roller. But,Too thinAnd insufficient strength. Further, similarly to the film fixing described later, a problem of non-sheet passing portion temperature rise occurs.
[0008]
b. Film heating method
This has a heating element and a film in which one surface slides on the heating element and the other surface moves in contact with the recording material. The heat of the heating element is applied to the recording material through the film to be determined. This is a device that heats and fixes a toner image on the recording material surface (JP-A-63-313182, JP-A-2-157878, JP-A-4-44075-44083, 204980-204984, etc.).
[0009]
Such a film heating type apparatus can use a low heat capacity ceramic heater or the like as a heating body, and a heat resistant thin thin heat capacity apparatus as a film, and a heat roller type apparatus using a fixing roller having a large heat capacity. Compared to the above, there are advantages such as significantly reduced power consumption and shortened wait time, quick start performance, and suppression of temperature rise in the machine.
[0010]
c. Electromagnetic induction heating method
This is because an electromagnetic induction heating element is used as a heating element, and a magnetic field is applied to the electromagnetic induction heating element by a magnetic field generating means, and Joule heating based on eddy currents generated in the electromagnetic induction heating element is used as a recording material as a material to be heated. This is a device that heat-fixes an unfixed toner image on a recording material surface by applying heat.
[0011]
Japanese Examined Patent Publication No. 5-9027 discloses a heat roller type apparatus that electromagnetically heats a ferromagnetic fixing roller. The heat generating position can be close to the fixing nip, and a halogen lamp is used as a heat source. It achieves a fixing process that is more efficient than the conventional heat roller system.
[0012]
However, since the heat capacity of the fixing roller is large, there is a problem that a large amount of electric power is required to raise the temperature of the fixing nip portion with limited electric power. One solution to this problem is to reduce the heat capacity of the fixing roller. For example, reducing the thickness of the fixing roller.
[0013]
Japanese Patent Application Laid-Open No. 4-166966 discloses an electromagnetic induction heating type fixing device using a film-like fixing roller (film) with reduced heat capacity.
[0014]
However, in a film-like fixing roller (film) with a reduced heat capacity, the heat flow in the long direction (the longitudinal direction of the fixing nip portion) is obstructed. Therefore, when a small-size recording material is passed, An excessive temperature rise (non-sheet passing portion temperature rise) has occurred, causing a problem of reducing the life of the film and the pressure roller. The problem of the temperature rise of the non-sheet passing portion is the same as in the case of the film heating type apparatus of the item b.
[0015]
Japanese Patent Laid-Open Nos. 9-171889 and 10-74009 have magnetic flux adjusting means for changing the density distribution of the acting magnetic flux from the magnetic flux generating means in the longitudinal direction of the fixing roller (film) to the induction heating element. A heating device is disclosed. One method for solving the non-sheet passing portion temperature rise by the electromagnetic induction heating type fixing device has been shown.
[0016]
Japanese Patent Application Laid-Open Nos. 9-171889 and 10-74009 use a configuration in which a film-like induction heating element is heated as an example, but a configuration in which a cylindrical induction heating element is used as a fixing roller is also used. This is considered to be effective as a countermeasure for the problem of temperature rise in the non-sheet passing portion.
[0017]
As another method for solving the temperature increase in the non-sheet passing portion, there is a method in which the fixing speed is decreased when a small size recording material is passed (throughput reduction). By slowing down the fixing speed, the heat transfer time in the end direction (non-sheet passing portion) of the fixing roller is provided. However, this method reduces the productivity of the image forming apparatus.
[0018]
[Problems to be solved by the invention]
  The present invention is an electromagnetic induction heating method of the item c in particular among the above, and uses a magnetic flux shielding means as a countermeasure against temperature rise of the non-sheet passing portion.imageConcerning further improvements to the heating device, while reducing the standby space of the magnetic flux shielding member and the space of the drive means, a compact magnetic flux shielding mechanism is constructed to save space (compact) and reduce the cost of the device. , Improved power saving and productivityimageA heating device is realized.
[0019]
[Means for Solving the Problems]
  The present invention is characterized by the following configuration.imageHeating equipmentIn placeis there.
[0020]
  (1) An image heating apparatus having an exciting coil that generates magnetic flux and a heating element having a heat generating part that generates heat by induction from the magnetic flux from the exciting coil, and heats an image on a recording material by the heat of the heating element An image heating apparatus having a conductive and nonmagnetic magnetic flux shielding member that shields magnetic flux generated from the exciting coil, and a moving means that moves the magnetic flux shielding member.
  The exciting coilIs disposed on the side opposite to the side facing the heat generating portion, and forms a path for magnetic flux generated from the exciting coil.Having a magnetic core,
  The moving means moves the magnetic flux shielding member between the magnetic core and the exciting coil.BeforeMagnetic flux shielding memberOf the area corresponding to the position whereAn image heating apparatus that reduces magnetic flux acting on the heat generating portion.
[0021]
  (2)An image heating apparatus comprising: an excitation coil that generates magnetic flux; and a heating element having a heat generating portion that generates heat by induction of magnetic flux from the excitation coil, and heats an image on a recording material by heat of the heating element. A conductive and non-magnetic flux shielding member for shielding magnetic flux generated from the exciting coil;,In an image heating apparatus having a moving means for moving the magnetic flux shielding member,
  Arranged on the opposite side of the exciting coil to the side facing the heat generating portion, opposite to the magnetic core forming a path for magnetic flux generated from the exciting coil, and opposed to the heating element together with the exciting coil And a heating element counter magnetic body core that forms a path of magnetic flux generated from the exciting coil,
  The moving means makes the magnetic flux shielding member face the opposite magnetic core and the heating element.Move between the magnetic coreThis reduces the magnetic flux acting on the heat generating part in the region corresponding to the position where the magnetic flux shielding member has moved.It is characterized byStatueHeating device.
[0035]
DETAILED DESCRIPTION OF THE INVENTION
[First embodiment]
(1) Example of image forming apparatus
FIG. 1 is a schematic diagram of a configuration of an image forming apparatus 100 in the present embodiment. The image forming apparatus 100 according to this embodiment is a laser copying machine using a transfer type electrophotographic process.
[0036]
Reference numeral 101 denotes an original platen glass. An original O is placed on the original platen glass 101 with the image surface facing downward according to a predetermined placement standard, and the original cover 102 is placed on the original plate. When the copy start key is pressed, the image photoelectric reading device (reader unit) 103 including the moving optical system operates to photoelectrically read the image information on the downward image surface of the document O on the document table glass 101. An original document feeder (ADF, RDF) may be mounted on the platen glass 101 to automatically feed the document onto the platen glass 101.
[0037]
Reference numeral 104 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum), which is rotationally driven at a predetermined peripheral speed in the clockwise direction of an arrow. The photosensitive drum 104 is uniformly charged with a predetermined polarity and potential by the charging device 105 during the rotation process, and is uniformly charged by receiving image exposure L by the image writing device 106 on the uniformly charged surface. The potential of the exposed bright portion of the surface is attenuated, and an electrostatic latent image corresponding to the exposure pattern is formed on the surface of the photosensitive drum 104. In this example, the image writing device 106 is a laser scanner, and is modulated in response to a time-series electric digital pixel signal of document image information photoelectrically read by the photoelectric reading device 103 in accordance with a command from a controller (not shown). The laser beam L is output, and the uniformly charged surface of the rotating photosensitive drum 104 is scanned and exposed to form an electrostatic latent image corresponding to the document image information.
[0038]
Next, the electrostatic latent image is developed as a toner image by the developing device 107, and at the position of the transfer charging device 108, a predetermined portion is applied from the paper feeding mechanism portion side to a transfer portion that is a facing portion between the photosensitive drum 104 and the transfer charging device 108. Is electrostatically transferred from the surface of the photosensitive drum 104 to the recording material S fed at the control timing.
[0039]
In the case of the image forming apparatus of this example, the sheet feeding mechanism section includes first to fourth cassette sheet feeding sections 109 to 112, an MP tray (multi-purpose tray) 113, and a reverse refeed section 114. From there, the recording material S is selectively fed to the transfer section. Reference numeral 115 denotes a registration roller for timing-feeding the recording material to the transfer unit.
[0040]
The recording material that has received the transfer of the toner image from the surface of the photosensitive drum 104 at the transfer unit is separated from the surface of the photosensitive drum 104, transported to the fixing device 116, and subjected to fixing processing of the unfixed toner image. The paper is discharged onto a paper discharge tray 118 outside the apparatus.
[0041]
On the other hand, the surface of the photosensitive drum 104 after separation of the recording material is cleaned by the cleaning device 119 after removal of adhering contaminants such as toner remaining after transfer, and is repeatedly used for image formation.
[0042]
In the double-sided copy mode, the recording material copied on the first side from the fixing device 116 is introduced into the reverse refeeding unit 114 and reversely fed back to the transfer unit, whereby the second side of the recording material is supplied. The toner image is transferred, and again passes through the fixing device 116 and is discharged as a double-sided copy onto a discharge tray 118 outside the apparatus by a discharge roller 117.
[0043]
The copying machine of this embodiment is a multi-function machine having a printer function and a facsimile function. However, since it is out of the gist of the present invention, its description is omitted.
[0044]
(2) Fixing device 116
FIG. 2 is a longitudinal cross-sectional model view (the apparatus longitudinal direction) of the fixing device 116, and FIG. 3 is a transverse cross-sectional model view (apparatus short direction). This fixing device 116 is an electromagnetic induction heating method according to the present invention, and is a magnetic flux adjustment type heating device using magnetic flux shielding means.
[0045]
7 is a cylindrical fixing roller as an induction heating element that generates electromagnetic induction heat, and is rotatably held between the apparatus side plates 25a and 25b via bearings (bearings) 21a and 21b. The fixing roller 7 is preferably made of a metal such as iron, nickel, or cobalt. By using a ferromagnetic metal (a metal having a high magnetic permeability), the magnetic flux generated from the magnetic flux generating means can be more restricted in the ferromagnetic metal. That is, the magnetic flux density can be increased. Thereby, an eddy current is efficiently generated on the surface of the ferromagnetic metal to generate heat. The heat capacity is reduced by setting the thickness of the fixing roller 7 to about 0.3 to 2 mm. A toner release layer (not shown) is provided on the outer surface of the fixing roller 7. Generally, it is comprised by PTFE 10-50 micrometers or PFA 10-50 micrometers. Further, a rubber layer may be used inside the toner release layer.
[0046]
Reference numeral 1 denotes a magnetic flux adjusting type heating assembly disposed in the fixing roller 7 and includes magnetic flux generating means 5 and 6 (ac), magnetic flux adjusting means 3 (a and b) and 4. The configuration of the heating assembly 1 will be described in detail in the next section (3).
[0047]
An elastic pressure roller 8 is arranged below the fixing roller 7 in parallel with the fixing roller. The elastic pressure roller 8 is rotatably held between the bearings 31a and 31b and urges (not shown) against the lower surface of the fixing roller 7. The fixing nip portion N as a heating portion having a predetermined width is formed by pressing with a predetermined pressing force against elasticity by the means. The pressure roller 8 has a configuration in which a silicone rubber layer and a toner release layer are provided on the outer periphery of an iron core bar in the same manner as the fixing roller 7.
[0048]
The fixing roller 7 is rotationally driven at a predetermined peripheral speed in the clockwise direction A of FIG. 3 by transmitting a rotational force from a driving system (not shown) to a fixing roller gear 18 fixed to one end thereof. . The pressure roller 8 is rotated in the counterclockwise direction B indicated by the arrow following the rotational driving of the fixing roller 7.
[0049]
  Electric power (high-frequency current) is supplied from the power control device (excitation circuit) 25 through the coil supply line 15 to the excitation coil 5 of the heating assembly 1 disposed in the fixing roller 7, and thereby magnetic flux generated from the heating assembly 1. Due to the action of the alternating magnetic field, the fixing roller 7 as an induction heating element generates induction heat (Joule heat due to eddy current loss). The temperature of the fixing roller 7 is detected by a first temperature detecting means (such as a thermistor) 32, and the detected temperature signal is input to the control circuit 34. The control circuit 34firstThe power supply from the power control device 25 to the exciting coil 5 of the heating assembly 1 is controlled so that the detected temperature of the fixing roller 7 inputted from the temperature detecting means 32 is maintained at a predetermined fixing temperature, so that the temperature of the fixing roller is increased. Adjust.
[0050]
In the state in which the fixing roller 7 and the pressure roller 8 are rotationally driven as described above and the fixing roller 7 is inductively heated by the power supply to the excitation coil 5 of the heating assembly 1 and is adjusted to a predetermined fixing temperature. The recording material S carrying the unfixed toner image electrostatically transferred in the transfer section of the forming apparatus is introduced into the fixing nip section N of the fixing apparatus 116 from the direction of arrow C as shown in FIG. It is nipped and conveyed. In this nipping and conveying process, the unfixed toner image on the recording material S surface is fixed on the recording material S surface as a permanently fixed image by the heat and nip pressure of the fixing roller 7. Reference numeral 30 denotes a separation claw, which prevents the recording material introduced into the fixing nip portion N and exiting the fixing nip portion N from being wound around the fixing roller 7 and separated from the fixing roller 7.
[0051]
In this embodiment, the recording material S is passed through the fixing device 116 by central reference conveyance. In FIG. 2, W1 is the maximum size paper width of the recording material S with respect to the fixing device 116, W2 is the small size paper width, W3 and W3 are non-passage that occurs in the fixing nip portion N when the recording material S of the small size paper width W2 is passed. It is a paper portion and is a difference area between the maximum size paper width W1 and the small size paper width W2.
[0052]
In the fixing device 116 of this embodiment, the maximum size paper width W1 is A4 width (297 mm), and the small size paper width W2 is A4R (210 mm). In the apparatus of this embodiment, the maximum size paper width W1 is a normal paper size width, and W1 is hereinafter referred to as a normal paper size width.
[0053]
(3) Heating assembly 1
The heating assembly 1 includes, in a holder 2, an exciting coil 5 and a magnetic core 6 (a · b · c) that constitute magnetic flux generating means, and a magnetic flux shielding member 3 (a · b) that constitutes magnetic flux adjusting means. A lead screw member 4 or the like is incorporated as a moving means for movement.
[0054]
  The holder 2 has a substantially semicircular shape in cross section, and a holder is provided at a substantially central portion of the inner surface of the holder 2.ー lengthA first magnetic core 6a (hereinafter abbreviated as first core 6a) is disposed and held along the hand. The length dimension of the first core 6a is substantially the same as the normal paper size width W1, and is positioned corresponding to the normal paper size width portion.
[0055]
An exciting coil 5 (hereinafter abbreviated as “coil 5”) is also disposed and held on the inner surface of the holder 2 with the first core 6a as the winding center. The coil 5 is substantially elliptical in the longitudinal direction of the fixing roller 7 and has a shape along the inner surface of a cylindrical object such as the fixing roller 7. The coil 5 is characterized by a shape along the inner surface of the fixing roller 7 even in the U-turn portion. Thereby, the lead screw member 4 to be described later can be disposed close to the coil 5. The coil 5 is arranged along the inner peripheral surface of the holder 2.
[0056]
Reference numeral 19 denotes a holder cover having a substantially semicircular cross-sectional shape. The holder cover 19 is fitted on the holder 2 having the first core 6a and the coil 5 disposed therein as described above. The core 6a and the coil 5 are held down and held.
[0057]
Two second magnetic cores 6b and 6b (hereinafter abbreviated as second core 6b) are arranged and held on both longitudinal sides of the holder lid 19. The length dimension of the second core 6b is substantially the same as the normal paper size width W1, and is positioned corresponding to the normal paper size width portion.
[0058]
The lead screw member 4 is arranged in parallel with the holder lid 19 and is fitted into the substantially semicircular shape of the cross section of the center portion of the holder lid so that the axis is substantially coincident with the axis of the substantially semicircular shape. The shaft end portions 4c and 4d on the side and the other side are rotatably supported by bearing portions 2a and 2b at both ends of the holder 2, respectively. The bearing portions 2a and 2b may be separately provided with durable bearing members.
[0059]
The shaft portions on one end side and the other end side of the lead screw member 4 are opposite screw portions 4a and 4b. Further, a third magnetic core 6c (hereinafter abbreviated as the third core 6c) is provided at the central portion of the lead screw member between the screw portions 4a and 4b on the one end side and the other end side of the lead screw member 4. is there. The length dimension of the third core 6c is substantially the same as the normal paper size width W1, and is positioned corresponding to the normal paper size width portion. The third core 6 c is integrated with the lead screw member 4 by bonding, patching, or the like at a core set portion provided on the lead screw member 4. Further, it may be integrally formed by resin molding. The present invention does not define the connection between the lead screw member and the core.
[0060]
Configure magnetic flux generation meansMagneticThe sex core 6 is divided into the first core 6a, the two second cores 6b and 6b, and the third core 6c that are parallel to each other as described above, and the cores 6a, 6b, and 6c thus divided are divided. Are used to form a magnetic flux path (magnetic circuit), and the magnetic flux shielding members 3a and 3b can be moved between the cores.
[0061]
  In the present embodiment, in the cross section of FIG. 3, the vertical portion is formed by the first core 6a at the winding center portion of the coil 5, the horizontal portion is formed by the two second cores 6b and 6b, and the third core 6c is further formed. Forms a substantially T-shaped central part, and the first to third three types of cores 6a, 6b, 6c form a substantially T-shaped core 6 in cross section, and the magnetic flux shielding members 3a, 3b When there is no intervention, the magnetic circuit Ja can be formed as shown in FIG. A magnetic field line Ja indicates a magnetic circuit of the generated magnetic field lines when electric power is input to the coil 5 from the power control device 25. The magnetic field lines Ja pass through the first core 6a (vertical portion), the fixing roller 7, the second core 6b (horizontal portion), and the third core 6c (center portion). Actually, the magnetic field lines pass through the inside of the fixing roller 7 having a high magnetic permeability, but are shown as shown in the figure for easy understanding.
  Here, the third core 6c corresponds to the “magnetic core” or the “opposite magnetic core” in claim 1 or 2. Further, the first core 6a or the second cores 6b and 6b, or the first core 6a or the second cores 6b and 6b correspond to the “heating element-facing magnetic core” in claim 2.
[0062]
  The third core 6c in the present embodiment is a core having a square cross section so that the influence of the rotation of the lead screw member 4 is small. Further, even if the rotation of the lead screw member 4 stops at a position where the position of the cross section is slightly inclined, the distribution of the fixing roller surface temperature does not change as the heat generation distribution in the longitudinal direction of the fixing roller 7 (as a whole). The heat generation efficiency of In this embodiment, a square cross-sectional shape is used. in short,SymmetryShape. Moreover, if it is a cylindrical core, the influence by rotation of the lead screw member 4 can be eliminated.
[0063]
In this embodiment, as shown in FIG. 2, the end portion of the first core 6 a is larger than the center portion, but this is a shape for compensating for heat escaping from the end portion of the fixing roller 7.
[0064]
Cylindrical magnetic flux shielding members 3a and 3b are fitted on the screw portions 4a and 4b on one end side and the other end side of the lead screw member 4, respectively, and the boss portion 3f is engaged with the screw portions 4a and 4b. . The magnetic flux shielding members 3a and 3b are stopped by a rotation prevention member (not shown). FIG. 4 is a schematic perspective view of the magnetic flux shielding member 3 (a · b). When the lead screw member 4 is driven to rotate forward a, the two magnetic flux shielding members 3a and 3b are thrust forward and moved along the lead screw member 4 in the direction toward the third core 6c. By rotating the member 4 in the reverse direction, the two magnetic flux shielding members 3a and 3b are thrust back and moved d in the direction away from the third core 6c along the lead screw member 4, respectively.
[0065]
The heating assembly 1, which is an assembly of the holder 2, the coil 5, the first core 6a, the holder lid 19, the second cores 6b and 6b, the third core 6c, the lead screw member 4, and the magnetic flux shielding members 3a and 3b, The engaging portions 2c and 2d at both ends of the holder 2 are respectively positioned on the support side plates 13 and 14 on the apparatus main body side and fixedly supported and fixedly inserted.
[0066]
The heating assembly 1 is in non-contact with the inner surface of the fixing roller 7 and the first core 6a is positioned obliquely downward on the upstream side of the fixing nip portion N in the rotational direction of the fixing roller 7 in the cross section of FIG. In the fixing roller 7.
[0067]
Further, the shaft portion 4c on one side of the lead screw member 4 is extended and protruded to the outside, the protruding shaft portion 4e is formed in a D shape, and the gear 11 is fixed, and the drive gear of the gear 11 and the drive motor 20 is fixed. 20a is meshed.
[0068]
The control circuit 34 controls the drive motor 20 through the driver 35 and drives the lead screw member 4 of the heating assembly 1 through the gears 20a and 11 in the normal rotation drive a or reverse drive b, so that the magnetic flux shielding members 3a and 3b. The movement position is switched to the first and second movement positions as will be described later.
[0069]
The coil 5 of the heating assembly 1 and the power control device 25 are electrically connected via the coil supply line 15.
[0070]
(1). First moving position of the magnetic flux shielding members 3a and 3b
When the lead screw member 4 is reversely driven b (FIG. 4), the two magnetic flux shielding members 3a and 3b are thrust back and moved in the direction away from the third core 6c along the lead screw member 4, respectively. As shown in FIG. 2, the positions where the magnetic flux shielding members 3a and 3b are moved back to the predetermined positions outside the both ends of the third core 6c are the first movement positions.
[0071]
The control circuit 34 normally waits for the magnetic flux shielding members 3a and 3b to move to the first movement position, and the recording material S (A4) having the normal paper size width W1 in which the non-sheet passing portion temperature does not rise is used. When this is done, the magnetic flux shielding members 3a and 3b are held in a state where they are kept waiting at the first movement position.
[0072]
When the magnetic flux shielding members 3a and 3b are in the first movement position, the magnetic flux in the magnetic circuit in the normal paper size width W1 region is not shielded by the magnetic flux shielding members 3a and 3b. The magnetic circuit can be a magnetic circuit Ja as shown in FIG.
[0073]
As a result, the heat generation distribution at the end of the normal paper size width W1 is as shown in FIG. 7B, and the heat generation distribution along the longitudinal direction of the fixing roller 7 is higher at the end. (3) in FIG. 7 is the fixing roller surface temperature at that time, and is made uniform in the longitudinal direction by offsetting with the edge sagging, and can be fixed over the entire width of the normal paper size width W1.
[0074]
(2). Second moving position of the magnetic flux shielding members 3a and 3b
When the lead screw member 4 is driven to rotate forward a, the two magnetic flux shielding members 3a and 3b are thrust forward and moved c along the lead screw member 4 toward the third core 6c, respectively. As described above, the second movement position of the magnetic flux shielding members 3a and 3b is a position where the magnetic core is moved forward to a portion corresponding to the non-sheet passing portions W3 and W3 on both end sides of the third core 6c.
[0075]
The control circuit 34 moves the magnetic flux shielding members 3a and 3b forward to the second moving position when the recording material S (A4R) having a small paper width W2 where the temperature rise in the non-sheet passing portion is used. Switch control.
[0076]
Thereby, the magnetic flux in the magnetic circuit in the small paper width W2 region where the magnetic flux shielding members 3a and 3b are not intervening is not shielded by the magnetic flux shielding members 3a and 3b. (A) is a magnetic circuit Ja. However, in the magnetic circuit in the non-sheet passing portion W3 / W3 area where the magnetic flux shielding members 3a and 3b intervene, the third core 6c portion corresponding to the non-sheet passing portion W3 / W3 area is covered with the magnetic flux shielding members 3a and 3b. As a result, the flow of magnetic flux inside the third core 6c corresponding to the non-sheet passing portions W3 and W3 is shielded, and the magnetic circuit Jb as shown in FIG. That is, the magnetic flux shielding members 3a and 3b obstruct the flow of magnetic flux in the non-sheet passing portions W3 and W3. As a result, as shown in FIG. 8, fixing is possible over the entire width of the small-size paper width W2, and heat generation due to electromagnetic induction is reduced in the non-sheet passing portions W3 and W3 of the fixing nip portion N. Temperature rise can be suppressed.
[0077]
As described above, the magnetic flux adjusting means thrusts the magnetic flux shielding members 3a and 3b when the recording material S (A4R) having the small paper width W2 in which the temperature rise at the non-sheet passing portion is used to pass the sheet. By placing the magnetic flux shielding members 3a and 3b between the three cores 6c, the first core 6a, and the second core 6b, the path of the magnetic flux passing back and forth between the cores is changed to generate electromagnetic induction heat in the fixing roller longitudinal direction. To control.
[0078]
It is known that the heat generation efficiency is better as the gap between the coil 5 and the fixing roller 7 which is an induction heating element is closer. Compared with the prior art, the present invention does not provide a magnetic flux shielding member in the gap between the coil 5 and the fixing roller 7, so that the heat generation efficiency can be improved.
[0079]
The first and second position switching of the magnetic flux shielding members 3a and 3b by the forward / reverse rotation control of the lead screw member 4 is automatically performed by the control circuit 34 depending on the size of the recording material used for passing the paper. When the paper size is determined, or the user designates the paper size and the paper is fed from the paper feed cassette in which the determined paper size is set, the control circuit 34 performs this. At that time, when the recording material to be fed has a paper size that causes the temperature rise of the non-sheet passing portion, the magnetic flux shielding members 3a and 3b are moved to the second movement position to raise the temperature of the non-sheet passing portion of the fixing roller 7. Is prevented.
[0080]
Further, in the image forming apparatus provided with a plurality of means for detecting the surface temperature of the fixing roller in the longitudinal direction, the temperature of the non-sheet passing portion can be detected and the magnetic flux shielding members 3a and 3b can be operated as required. Specifically, as shown in FIGS. 2 and 6, in addition to the first temperature detection means 32, the second temperature detection means 33 is provided at the position corresponding to the non-sheet passing portion as the surface temperature detection means of the fixing roller 7. The magnetic flux shielding members 3a and 3b may be controlled to move to the second position by detecting the temperature of the non-sheet passing portion. The first temperature detection means 32 is disposed at a position corresponding to the small size paper width.
[0081]
The present invention does not limit the operation sequence of the magnetic flux shielding members 3a and 3b.
[0082]
Further, when the sheet passing width size of the recording material S used for sheet passing is smaller than the normal sheet size width W1 (A4) and larger than the small size sheet width W2 (A4R) (for example, B4 = 257 mm), The stepless movement control of the magnetic flux shielding members 3a and 3b can be performed in accordance with the sheet passing width size. The present invention does not limit the operation sequence of the magnetic flux adjusting means.
[0083]
The magnetic flux shielding members 3a and 3b are made of non-magnetic and well-conductive members. By using a non-magnetic member, there is an effect of blocking magnetic flux. By using a good electrical conductive member, there is an effect of suppressing heat generation by electromagnetic induction of the magnetic flux shielding member itself. In this embodiment, an aluminum alloy is used, but an alloy of copper, magnesium, silver, or the like may be used.
[0084]
The thickness of the magnetic flux shielding members 3a and 3b may be about 0.3 to 1.0 mm. If it is too thin, the magnetic flux shielding member itself generates electromagnetic induction heat. In addition, the strength is insufficient. On the other hand, if the thickness is too thick, the heat capacity of the magnetic flux shielding member increases, and when the fixing roller is heated, the heat is taken away, leading to an increase in the wait time.
[0085]
The lead screw member 4 and holder 2 are made of PPS resin, PEEK resin, polyimide resin, polyamide resin, polyamideimide resin, ceramic, liquid crystal polymer, fluorine resin, etc. that have both heat resistance and mechanical strength. The substance is suitable. Furthermore, those obtained by adding glass to these resins are used. If the lead screw member and the holder inside the magnetic flux generating means are made of a magnetic material, the lead screw member and the holder generate heat due to electromagnetic induction, and the heat generation efficiency of the fixing roller decreases. In the case of using a metal other than the resin, a decrease in heat generation efficiency can be suppressed by selecting a non-magnetic, good electrical conductive material.
[0086]
The coil 5 must generate an alternating magnetic flux sufficient for heating. For this purpose, it is necessary to make the resistance component low and the inductance component high. As a core wire of the coil, a litz wire in which about 80 to 160 fine wires having a diameter of 0.1 to 0.3 are bundled is used. Insulated coated wires are used for the thin wires. The coil 5 is formed by winding 8 to 12 times so as to go around the first core 6a. An excitation circuit is connected to the coil 5 so that an alternating current can be supplied to the coil 5.
[0087]
As the core 6 (ac), it is preferable to use a material having high permeability and low residual magnetic flux density such as ferrite and permalloy, but it is not particularly limited as long as it can generate magnetic flux.
[0088]
The present invention does not limit the shape / material of the fixing roller as the coil / core / induction heating element of the magnetic flux generating means.
[0089]
  Second, second belowThirdThe embodiment shows a variation of the third core 6c provided on the lead screw member 4 of the fixing device of the first embodiment.
[0090]
The magnetic flux generating means can control the heat generation efficiency by changing the shape and arrangement of the core. By using the present invention, the degree of freedom in designing the core shape and arrangement is widened, and a fixing device corresponding to many specifications of the main body can be made.
[0091]
[Second Example]
In the second embodiment, as shown in FIG. 9, the third core 6c has a cross-shaped cross shape. By using a cross core, the distance between the first core 6a and the second core 6b can be shortened, so the heat generation efficiency is good. The third core 6c having a T-shaped cross section can obtain the same heat generation efficiency, but the cross-shaped configuration can reduce the influence of the rotation of the lead screw member 4. This is because the lead screw member 4 has a core shape with the same cross section every 90 degrees.
[0092]
[Third embodiment]
In the third embodiment, the third core 6c is I-shaped as shown in FIG. The second cores 6b and 6b are not provided. Although the heat generation efficiency is inferior to that of the above embodiment, the cost can be reduced by simplifying the core member, the holder 2 and the holder lid 19.
[0093]
By controlling the rotational speed of the lead screw member 4 of the first, second, and third embodiments and changing the pitch of the lead screw portions 4a and 4b, when there is no temperature rise in the non-sheet passing portion (during standby) The same core cross section can be obtained when the magnetic flux shielding members 3a and 3b are moving. For example, in the third embodiment, the thrust movement amount is limited by controlling the rotation of the lead screw member 4 every 90 degrees, but the cross-sectional core shape can be made the same as in the standby state. Also, the pitch of the lead screw portions 4a and 4b can be set to a frequently used paper size.
[0094]
  [Reference example]
  thisReference exampleAs shown in FIGS. 11 and 12, the lead screw member 4 is not provided with the third core 6c. Accordingly, as shown in FIG. 12, the magnetic core 6 of the magnetic flux generating means is composed of a first core 6a and second cores 6b and 6b.
  1)When the recording material S (A4) having the normal paper size width W1 in which the temperature rise of the non-sheet passing portion does not occur is used, the magnetic flux shielding members 3a and 3b are kept waiting at the first movement position indicated by the solid line in FIG. Keep in state.
[0095]
When the magnetic flux shielding members 3a and 3b are in the first movement position, the magnetic flux in the magnetic circuit in the normal paper size width W1 region is not shielded by the magnetic flux shielding members 3a and 3b. The magnetic circuit can be a magnetic circuit Ja as shown in FIG. As a result, the heat generation distribution at the end of the normal paper size width W1 is as shown in FIG. 7B, and the heat generation distribution along the longitudinal direction of the fixing roller 7 is higher at the end. (3) in FIG. 7 is that the surface temperature of the fixing roller at that time is uniform in the longitudinal direction, and fixing is possible with the entire width of the normal paper size width W1.
[0096]
  2)When the recording material S (A4R) having a small-size paper width W2 where the temperature rise in the non-sheet passing portion is used, the magnetic flux shielding members 3a and 3b are moved forward to the second moving position indicated by the two-dot chain line in FIG. Control to switch to the state.
[0097]
As a result, the magnetic flux in the magnetic circuit in the small size paper width W2 region where the magnetic flux shielding members 3a and 3b are not intervening is not shielded by the magnetic flux shielding members 3a and 3b. (A) is a magnetic circuit Ja.
[0098]
However, the magnetic circuit in the non-sheet passing portion W3 / W3 region where the magnetic flux shielding members 3a and 3b intervene is the magnetic flux between the first core 6a portion and the second core 6b portion corresponding to the non-sheet passing portion W3 / W3 region. As a result, the magnetic circuit Jb as shown in FIG. 12B is obtained. That is, the magnetic flux shielding members 3a and 3b obstruct the flow of magnetic flux in the non-sheet passing portions W3 and W3. As a result, as shown in FIG. 8, fixing is possible over the entire width of the small-size paper width W2, and heat generation due to electromagnetic induction is reduced in the non-sheet passing portions W3 and W3 of the fixing nip portion N. Temperature rise can be suppressed.
[0099]
  in this wayReference exampleHowever, similarly to the above embodiment, the magnetic flux shielding members 3a and 3b are thrust-moved to inhibit the flow of magnetic flux between the first core 6a and the second core 6b, and the heat generation efficiency in the longitudinal direction is changed to change the fixing roller. The longitudinal distribution of surface temperature can be changed.
[0100]
  AlsoReference exampleThen, as shown in FIG. 11, the screw portions 4a and 4b of the lead screw member 4 can be formed up to the center portion of the fixing roller, so that the width corresponding to the paper size can be increased.
[0101]
  Further, even in the magnetic flux generating means (air core coil) having no core, by moving the magnetic flux shielding members 3a and 3b and placing them inside the coil 5, the above-mentionedReference exampleSimilarly, the heat generation efficiency can be changed in the longitudinal direction.
[0102]
In short, the heat distribution in the longitudinal direction of the fixing roller can be changed by changing the flow of the magnetic flux inside the coil 5 in the longitudinal direction.
[0103]
  [Fourth embodiment]
  This embodiment is an embodiment in which the diameter of the lead screw member 4 is increased and a third core 6c is provided inside the lead screw member 4 as shown in FIGS.
[0104]
Thus, it is not necessary to provide the cylindrical magnetic flux shielding members 3a and 3b as in the first embodiment, and the engagement with the screw portions 4a and 4b of the lead screw member 4 as shown in FIGS. Only the magnetic flux shielding member 3 of the matching portion 3f is required. Space saving in the longitudinal direction is possible.
[0105]
  Also in this embodiment, as in the above-described reference example, as shown in FIG. 14, the screw portions 4a and 4b of the lead screw member 4 can be formed up to the center portion of the fixing roller. .
[0106]
  As above4 typesHowever, the present invention may be used in a timely manner depending on the specifications of the image forming apparatus and the arrangement of the fixing device.
[0107]
Further, the effect of the present invention does not change even if a fixing film is used instead of the fixing roller.
[0108]
The effects of the fixing devices of the above embodiments as the heating device according to the present invention are summarized as follows.
[0109]
By providing magnetic flux shielding members 3a and 3b that shield (inhibit) the magnetic flux on the side opposite to the side facing the fixing roller 7 where the coil 5 is an induction heating element, the gap (gap) between the coil 5 and the fixing roller 7 is reduced. It is possible to save energy by improving the heat generation efficiency.
[0110]
Moreover, space saving can be performed by providing in the other side.
[0111]
Since the standby space of the magnetic flux shielding member can be reduced outside the fixing roller (or film), space saving can be realized and the size of the image forming apparatus main body can be reduced.
[0112]
In the conventional configuration in which the magnetic flux shielding member is rotationally moved, it is considered that the magnetic flux shielding member contacts the coil and breaks the coil. However, in the present invention, the contact between the coil and the magnetic flux shielding member can be eliminated.
[0113]
Conventionally, when the paper is fed in the center of the fixing film (central paper transport system), the standby space for the magnetic flux shielding member and the drive means space for the magnetic flux shielding member are required on both sides in the longitudinal direction of the fixing film. In the invention, since the magnetic flux shielding member is made to stand by inside the fixing roller and the driving means can be arranged on one side, space saving can be realized and the size of the image forming apparatus main body can be reduced.
[0114]
In the present invention, the temperature rise of the non-sheet passing portion can be solved without reducing the fixing speed, which leads to an improvement in image forming productivity.
[0115]
Since the magnetic flux generating means (coil / core), the holder, and the magnetic flux shielding member are configured as one assembly, it is possible to improve assemblability and serviceability.
[0116]
[Others]
1) The means for moving the magnetic flux shielding members 3a and 3b in the thrust direction is not limited to the lead screw member 4 or the like of the embodiment, and an appropriate mechanism configuration can be adopted. For example, it goes without saying that a well-known cylindrical cam with a cam groove that is often used in a zoom camera or the like may be used.
[0117]
2) The conveyance reference of the material to be heated may of course be the one-side conveyance reference, and the heating device is configured corresponding to the one-side conveyance reference.
[0118]
  3) The electromagnetic induction heating method and magnetic flux adjustment type of the present inventionimageThe heating device is not only an image heating and fixing device as in the embodiments, but also, for example, an image heating device that heats a recording material carrying an image to improve the surface properties such as gloss, and an image heating for hypothetical processing DressPlaceCan be used widely.
[0119]
【The invention's effect】
  As described above, according to the present invention, the electromagnetic induction heating method is used, and the magnetic flux shielding means is used as a countermeasure for raising the temperature of the non-sheet passing portion.imageConcerning the heating device, the space for waiting for the magnetic flux shielding member and the space for the drive means are reduced, and a compact magnetic flux shielding mechanism is constructed to save space and reduce the cost of the device while improving power saving and productivity.imageA heating device can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment.
[Fig. 2] Fixing device (electromagnetic induction heating typeimageModel of longitudinal section of heating device (magnetic flux shielding member-first movement position)
[Figure 3] Cross-sectional model view
FIG. 4 is a perspective model view of a magnetic flux shielding member portion on one side.
FIG. 5 is a conceptual diagram of a magnetic circuit of a portion where a magnetic flux shielding member is not interposed and an interposed portion.
FIG. 6 is a schematic longitudinal sectional view of the fixing device (magnetic flux shielding member—second moving position).
FIG. 7 is an explanatory diagram of the core arrangement, the heat generation distribution, and the surface temperature distribution of the fixing roller when the magnetic flux shielding member is in the first movement position.
FIG. 8 is an explanatory diagram of the core arrangement, the heat generation distribution, and the surface temperature distribution of the fixing roller when the magnetic flux shielding member is in the second movement position.
FIG. 9 is a schematic cross-sectional view of a fixing roller in a second embodiment.
FIG. 10 is a schematic cross-sectional view of a fixing roller according to a third embodiment.
FIG. 11Reference exampleModel of the vertical section of the fixing device (magnetic flux shielding member-first movement position)
FIG. 12 is a conceptual diagram of a magnetic circuit of a portion where a magnetic flux shielding member is not interposed and a portion where the magnetic flux shielding member is interposed
FIG. 13FourthFig. 8 is a schematic longitudinal sectional view of the fixing device in the embodiment (magnetic flux shielding member-first movement position).
FIG. 14 is an image diagram of a magnetic circuit in a portion where a magnetic flux shielding member is interposed.
[Explanation of symbols]
1. Magnetic flux adjustment heating assembly, 2. Holder, 3 (a, b), Magnetic flux shielding member, 4. Lead screw member, 5. Excitation coil, 6 (ac), Magnetic core, 7 .... Fixing roller, 8 .... Pressure roller, 11 .... Gear, 15 .... Coil power supply line, 21 (a.b) .. Bearing, N..Fixing nip, J (a.b).・ Magnetic lines of force in magnetic flux generator (magnetic circuit)

Claims (2)

An image heating apparatus comprising: an excitation coil that generates magnetic flux; and a heating element having a heat generating portion that generates heat by induction of magnetic flux from the excitation coil, and heats an image on a recording material by heat of the heating element. In an image heating apparatus having a conductive and nonmagnetic magnetic flux shielding member that shields magnetic flux generated from the exciting coil, and a moving means that moves the magnetic flux shielding member,
A magnetic core that is disposed on the opposite side of the exciting coil from the side facing the heat generating portion and forms a path of magnetic flux generated from the exciting coil ;
It said moving means to reduce the magnetic flux acting on the heating portion of the area corresponding to the position where the front Symbol magnetic flux shielding member is moved by moving between the exciting coil and the magnetic core of the magnetic flux shielding member An image heating apparatus. An image heating apparatus comprising: an excitation coil that generates magnetic flux; and a heating element having a heat generating portion that generates heat by induction of magnetic flux from the excitation coil, and heats an image on a recording material by heat of the heating element. In an image heating apparatus having a conductive and nonmagnetic magnetic flux shielding member that shields magnetic flux generated from the exciting coil, and a moving means that moves the magnetic flux shielding member,
Arranged on the opposite side of the exciting coil to the side facing the heat generating portion, opposite to the magnetic core forming a path for magnetic flux generated from the exciting coil, and opposed to the heating element together with the exciting coil And a heating element counter magnetic body core that forms a path of magnetic flux generated from the exciting coil,
The moving means moves the magnetic flux shielding member between the opposite magnetic body core and the heating element opposing magnetic body core, thereby acting on the heat generating portion in a region corresponding to the position where the magnetic flux shielding member has moved. an image heating apparatus thereby to reduce the magnetic flux.

Images